This project will investigate the proposed role of ras proteins in regulation of growth and development of eukaryotic cells. The filamentous fungus, Mucor racemosus, is induced to undergo three characteristic types of cellular morphogenesis in response to changes in growth conditions, nutrients, or gaseous environment and provides a simple model system of eukaryotic cell development which is amenable to biochemical and genetic analysis. The accumulated mRNA levels of 3 Mucor ras genes (MRAS) have been analyzed during several different stages of cell development. Two of the genes, MRAS1 and MRAS3 are differentially expressed during cell development in this fungus suggesting that these genes play a role in the developmental processes. The MRAS3 gene for example is expressed almost exclusively during asexual sporulation, while MRAS1 is expressed at highest levels in "rapidly" dividing hyphal cells or cells converting to hyphae. The MRAS1 and MRAS3 genes have unique temporal patterns of expression which may suggest that they play different roles in growth and development of the organism. Based on nucleotide sequence analyses, the proteins encoded by the MRAS genes are highly similar in amino acid sequence and size to the H- ras gene of higher eukaryotes which has been implicated in the regulation of cell growth and differentiation. Because of this protein similarity, understanding of ras function in regard to regulation of cell differentiation in these simple eukaryotic cells may lead to important insights into cell proliferation, differentiation and malfunctions in these processes which occur in mammalian tumors. The specific aims of this research proposal are: 1) to characterize the expression of the ras gene family (MRAS) in M. racemosus; 2) to alter the normal expression patter of ras genes in M. racemosos using MRAS expression vectors; 3) to characterize the effects of altered MRAS expression on morphogenesis, cell proliferation, and the biochemical changes which accompany these processes in M. racemosus. Normal ras expression and protein activity will be altered by transforming Mucor cells with plasmid constructs designed to alter MRAS protein structure, quantity, and temporal pattern of expression. Direct observation will detect phenotypic changes in the morphogenetic response or growth rates, while biochemical assays will be used to measure the effects of altered ras expression on cAMP metabolism and/or phosphoinositid metabolism.